The Ets-domain family of transcription factors is comprised of several proteins that are involved in controlling key cellular events such as proliferation, differentiation, and development. Their activity is often regulated by signal transduction pathways involving MAP kinases and, in regard to disease, the deregulation or mutation of Ets proteins is found primarily in cancers.
While the Ets family is very diverse in protein sequence, all of the family members share a DNA binding domain known as the Ets-domain, so called because it resembles the protein product of the v-ets oncogene of the E26 avian erythroblastosis virus. Through this motif, the Ets family proteins bind the promoter region of various genes at the consensus sequence, GGA, thereby acting as either repressors or activators through DNA-protein interactions and/or protein-protein interactions. All members of the family, except one, bind to DNA as a monomer and based on the homology within the Ets domain the Ets proteins have been further divided into subfamilies (Dittmer and Nordheim, Biochim. Biophys. Acta, 1998, 1377, F1-11).
ELK-1 (also known as p62TCF), first cloned in 1989, is a member of the ternary complex factor (TCF) subfamily of Ets domain proteins and utilizes a bipartite recognition mechanism mediated by both protein-DNA and protein-protein interactions. This results in gene regulation not only by direct DNA binding but also by indirect DNA binding through recruitment by other factors (Rao et al., Science, 1989, 244, 66-70). The formation of ternary complexes with an array of proteins allows the differential regulation of many genes. The mechanism by which ELK-1 controls various signal transduction pathways involves regulating the activity of the Egr-1, pip92, nur77 and c-fos promoters by binding to the serum response element (SRE) in these promoters in response to extracellular stimuli such as growth factors, mitogens and oncogene products (Sharrocks et al., Int. J. Biochem. Cell Biol., 1997, 29, 1371-1387). ELK-1 has also been shown to mediate other functions within the cell including apoptosis. Constitutive expression of ELK-1 was shown to trigger apoptosis in fibroblasts and breast cancer cells treated with a calcium ionophore (Shao et al., Oncogene, 1998, 17, 527-532).
Upstream, the regulation and transcriptional activity of ELK-1 is controlled by the phosphorylation state of the protein. ELK-1 is a substrate for the Ras/Raf/ERK pathway, induced by growth factors and the JNK and p38 MAP kinase pathways which are induced by environmental stresses (Sharrocks et al., Int. J. Biochem. Cell Biol., 1997, 29, 1371-1387).
To date, strategies aimed at inhibiting ELK-1 function have involved the use of inhibitors of the upstream kinase pathways including the specific inhibitor of MAP kinase, PD98059 (Weiss et al., Am. J. Physiol., 1998, 274, C1521-1529). However, these strategies are not specific to ELK-1, as many downstream regulatory events are affected by the MAPK, p38 and JNK kinase pathways.
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of ELK-1. Consequently, there remains a long felt need for additional agents capable of effectively inhibiting ELK-1 function.
Antisense oligonucleotides, however, provide a promising new pharmaceutical tool for the effective modification of the expression of specific genes.